1. Field of the Invention
This invention relates to a process for producing terephthalic acid by oxidizing para-xylene with molecular oxygen.
2. Description of the Prior Art
Oxidation of para-xylene with molecular oxygen in acetic acid as solvent in the presence of a catalyst system containing bromine and one or more heavy metals such as cobalt, manganese and the like for the preparation of terephthalic acid is well known as the S.D. method. Although this method is satisfactory for the commercial production of terephthalic acid in various respects, there is a problem in that loss of acetic acid as the solvent takes place during the reaction, resulting in enhanced solvent unit, which is a significant disadvantage of the method.
For this acetic acid loss, the following two principal causes are considered: the combustion of acetic acid and the formation of a by-product methyl acetate. Among these, the combustion of acetic acid has previously been investigated in various ways. It has been proposed, for example, to suppress the combustion using specific reaction conditions or a specific catalyst and a certain degree of good results have been obtained thereby. However, the other principal cause for the solvent loss, that is, the formation of the by-product methyl acetate has received little investigation.